However i have no real info on what you referred to ( FAST companies). Thus i will rely on the info i have. Bear with me.
Anyways (after that long aside) what i was trying to say is that based on the scenario the Russians were facing (i.e: terrorists start killing people, with half of the terrorists having their fingers on triggers to explosives with ball bearings strapped to their bodies, not to mention the mines lining the theater ..although i have to say in my opinion the kamikaze terrorists with strap-on explosives were the bigger threat). The Spetsgruppa al'fa had to act immediately, and thus they did not have the time to set up elaborate plans like the thermal detectors and radar systems you mentioned.
Compare this witht he example i gave of the 1980 Iranian embassy fiasco in London that the SAS had to handle. They had 11 weeks (almost 3 months) to train, which included building a replica of the embassy, and they were facing 6 terrorists armed with submachine guns and 26 hostages. The Russians on the other hand had minutes after the terrorists started killing hostages, and they had around 50 terrorists (with half scattered around the hostages with strapped on explosives on a hair trigger), plus around 750 hostages (meaning a bigger number of people to allocate 'friend or foe', all in a matter of seconds). The Russians were facing an uphill battle, and the very fact the terrorists did not manage to detonate the kamikaze bombs is a factor that is important because the death toll would have been tremendous.
As for the 'sleepingg as' i think it is some type of binary nerve agent (eg a sterease inhibitor) that was used to conk out the terrorists almost simulatenously. After all if they used a simple sleeping gas some terrorists would have noticed their fellow terrorists dozing off and exploded the bombs. Thus they had to use the nerve agent, and i am certain some of the 90 hostages dead demised due to the nerve agent (after all when your brain cannot communicate with your muscles there is a chance you can choke on your vomit ...and woe betide you if you are old). The reason i think the media says it is a 'sleeping gas' is because everyone was limp ....howevert he use of a sleeping gas would have been stupid. However release a nerve agent and voi'la .....Chechyan terrorists slumped on the floor to pump slugs into at pleasure!
Anyways my basic point was i am sure there are spec-ops teams that might have performed the job better. And i am sure if the Russian spetsgruppa had 11 weeks of practice like the SAS had, and if the terrorists had been armed with Kalashnikovs only instead of sucide bombs, and if the number of terrorists and hostages were lesser (eg 26 hostages like the SAS case instead of 750 hostages with half of the 50 terrorists wearing bombs and masquerading as hostages). And then provide mere minutes of reaction time.
To be honest with you i am surprised not many more hostages died, and i am especially surprised the Russians managed to nuetralize the kamikaze terrorists scattered among the hostages with strap-on bombs.
Hence i am sad 90 hostages died (and 30 terrorists to give a total of 120 dead ...although strangely the media is not emphasing it was 90 hostages 30 terrorists but are just saying 120 dead and putting the fact that 30 of that 120 is comprised of terrorists, but hey, i am not going to question the motives of the media). However i am impressed that under time and rpessure constraints the Russians managed to put a plan into work in minutes after they heard shots, and they managed to neutralize the terrorists without a greater death toll occuring.